As a preliminary point, it is appropriate to recall the meaning of the term “exoskeleton”, particularly as used in the context of the invention.
The term “exoskeleton” was originally used in biology for designating the outer supporting shell of an animal. For example, arthropods have an outer shell of chitin instead of an internal skeleton. More recently, the term has also been associated with structural devices designed to be attached around the limbs of people.
Still more recently, a new category of devices has been added to the family of exoskeletons: these are mechanisms used, for example, for the purpose of increasing the performance that can be delivered by a human, a robot, or indeed while interaction with virtual reality. Other possible applications for such mechanisms are described below.
By way of concrete example, the text below relates to the preferred application of the invention, specifically to its application to space technologies. Still more precisely, consideration is given to remotely controlling a humanoid type robot working outside a space station, for example the international space station. In the context of this application, the robot could be the robot known as “Eurobot” which is intended to provide highly accurate and dextrous means for performing inspection, maintenance, and repair actions on equipment in the highly hostile environment of space. The robot is fitted with three moving arms similar to human arms (i.e. in particular having seven degrees of freedom). Most of the time, the robot is programmed to perform pre-established tasks, but in some circumstances the robot needs to be remotely controlled:                either by astronauts inside the space station; or        else directly by operators who have remained on the earth.        
In both cases, the need to perform very precise manipulations makes it necessary to use so-called “immersion” techniques. For this purpose, the operator wears video goggles, force feedback gloves, and one or more arm exoskeletons so as to be able to feel the same sensations as the robot, i.e. the sensations which the operator would feel when performing the tasks that are being executed by the robot.
The need to create an exoskeleton compatible with operators on earth or with astronauts leads to various constraints. It is necessary for the system to be light in weight (typically less than 5 kilograms (kg)), compact, and easy to wear.
Exoskeletons in the state of the art generally suffer from various drawbacks and/or insufficiencies, such as the following:                it is not possible to feel all of the movements of the human arm and to obtain feedback forces and torques, without limiting the normal range of movements available to the human arm; it is in particular necessary to obtain information concerning the position of the shoulder, of the elbow, and of the wrist;        it is difficult to produce a system that is genuinely “portable”, which means that the movements of the operator should not be limited while the device is in use (turning around an article, leaning over, walking, etc.); and        limited ability to be fitted, which means, for example, that a given exoskeleton is not suitable for use with a high percentage of the male population, typically the 5th to 95th percentile range, without itself being significantly modified.        
More precisely, human arm exoskeletons need to overcome a major problem, namely that of imitating the movements of the complex human joints that are constituted by the shoulder, the elbow, and the wrist. Imitation is difficult because these joints are closely covered, with their axes of rotation moving with changing posture of the arm. In the state of the art, exoskeletons have attempted to deal with the problem of the shoulder by implementing a mechanism that rests on the human shoulder from above and behind. The imperfections of that approach can be found in the bulk and the weight of the mechanism. It also weighs down the arm. Similarly massive solutions have also been used for the wrist.
In general, it is also found that in known exoskeleton mechanisms, the complex movements of the joints of the human arm are simplified and reduced to joints having respective single degrees of freedom, or “DOF” in order to simplify description. The drawback of that solution is that normal movements of the “master” arm (i.e. the arm that imposes actions) is disturbed and it is not possible to achieve a sensation of comfort while the “slave” arm is in operation (force feedback).
Without being exhaustive, there follows a brief description of various known solutions, pointing out their limitations.
U.S. Pat. No. 4,575,297 A (Hans Richter) describes a robot having a chest plate, an upper arm member, and a lower arm member having finger and thumb units into which the human limbs are inserted. A human operator to whom the robot members are attached sits on a support structure such as a moving chair. The robot members, their lengths, the joints between them, and the joint axes correspond to those of the human operator. Each joint is associated with a hydraulic motor sensor device. The shoulder portion of the robot is restricted to movements about two axes. Another axis allows the elbow to flexed or to be extended. An axis parallel to the axis of the forearm allows the forearm to turn. On the wrist, a knuckle joint parallel to the swivel joint of the elbow provides means to enable the wrist to move in human manner.
The exoskeleton mechanism taught by the above-specified patent copies the normal movements of a human arm. Each actuated joint is controlled by hydraulic actuators, which are directly mounted beside the joints. The range of possible movements is relatively limited. In particular movement without backlash is not possible.
U.S. Pat. No. 5,967,580 A (Mark E. Rosheim) relates to a pair of connected-together joints and to force-generator means for using them in slave robot systems. The patent relates to an anthropomorphic mechanical manipulator providing some of the capabilities of a human torso and it can move in ways similar to the chest, the shoulder, the arm, the wrist, and the hands of a human. Again, the moving structure of the robot described in the above-specified patent resembles the moving structure of a human arm. It follows that it is desired to provide a mechanical manipulator resembling the upper human torso and the arm, and capable of being provided with movement options substantially equivalent to those available to the upper arm and torso of a human. A mechanical structure provides means for engaging the hands of an operator.
A counterpart mechanism can be used as an exoskeleton for controlling the slave robot, but it is not optimized for that use per se. It is possible to provide force feedback only in the portion of the exoskeleton that is equivalent to the hand. The two mechanisms are equivalent to the upper structure of a human limb in terms of movement (parameters of the limbs and the joints). Each axis of rotation is directly controlled by direct current (DC) linear motors. Only a very limited range of normal human movements of the arm can be covered with the exoskeleton mechanism as described. As mentioned above, force feedback is possible only for the human hand, with this characteristic being the main object of the patent.
U.S. Pat. No. 6,301,526 A (mun Sang Kim et al.) relates mainly to a device having a force feedback function and which is mounted on a human arm. This can return feedback information concerning operating limits by using motor brakes. The main device is a series type chain configuration fixed on the back of an operator. Second and third combining means are fixed above and below the elbow, and fourth combining means are fixed to a back portion of the hand. Seven axes of the exoskeleton include electric brake units for generating torque. Position-determining units and gear units for amplifying torque are associated with the actuator units.
The base of the moving system is fixed to the operator's back and not to the chest. The movement of the exoskeleton can be influenced only by passive electric brakes, which can be used only to damp the natural movements of the human arm.
International patent application WO 95/32842 A2 (AN, Bin) relates to a system having the same degrees of freedom as the human arm, and which therefore needs to be attached closely to the human arm. The system also moves in a manner equivalent to the arm of an operator. The exoskeleton is fixed on the operator's back and all the components that form an interface with the human body are adjustable. As a result, any misalignment between the operator and the system imparts movement constraints on the human joints and is very uncomfortable, impeding natural anatomic movements. That invention relates mainly to the problem of attaching the exoskeleton to the operator, which problem is solved by means of special design features.
Movements are restricted to only five degrees of freedom. Movements of the shoulder girdle, and movements of the wrist are neither detectable nor controllable. Each axis is actuated directly by a DC motor device, which is mounted close to an appropriate joint axis. Because of its highly simplified moving structure, many of the components need to be designed to be adjustable. The base of the exoskeleton is fixed on the upper portion of the operator's back.
It can be seen that prior art exoskeletons, some of which are described above, present major limitations and do not make it possible to satisfy fully the needs that are felt, in particular in space applications. Prior art exoskeletons are for the most part based on a mechanism which seeks to imitate or to approximate as closely as possible the movements of human limbs. Finally, as can be seen from the description below of the invention, prior art exoskeleton mechanisms present major structural differences compared with the mechanism implemented in the invention.